Compression brakes are well known devices in the industry used to provide additional stopping force especially in large vehicles. Internal combustion engines used on such vehicles typically have multiple cylinders, each of which defines a bore for receiving a piston. Each cylinder further includes one or more intake valves and one or more exhaust valves. During normal engine operation, the intake and exhaust valves are actuated at appropriate times to maximize the amount of force from fuel combustion that is delivered to an output, such as a crankshaft. A compression brake may alter the actuation of the intake and/or exhaust valves to dissipate the combustion force, thereby increasing engine drag to slow the vehicle. For example, in a standard four-cycle operation during a combustion stroke, an exhaust valve is generally in a closed position as a piston moves from near bottom dead center (BDC) to top dead center (TDC) and back to BDC. The force created by fuel combustion is therefore transferred to the crankshaft. During a compression brake operation during the combustion stroke, the exhaust valve generally opens as the piston moves from BDC to TDC and closes as the piston moves from TDC to BDC. Manipulating the valves in this manner dissipates any compression force during the upstroke, thereby dissipating the amount of force outputted to the crankshaft. Such systems are known in the art as compression release engine brakes.
A compression brake system is employed to actuate the intake and/or exhaust valves at the desired time, thereby to effect compression braking. The compression brake system typically includes a brake actuator, such as a brake actuator piston disposed in a brake actuator cylinder and mechanically coupled to the intake and/or exhaust valves. The actuator piston, in turn, may be hydraulically coupled to a master piston having a pin slidable between retracted and extended positions. A compression brake controller operatively coupled to the master piston may control flow of hydraulic fluid to the master piston, thereby to actuate the pin between the retracted and extended positions. A mechanical system may be used to couple the pin to a source of mechanical movement, such as a cam shaft.
The type of mechanical system used in the compression brake system may be influenced by the type of fuel injection system used by the vehicle engine. Some vehicles have mechanical unit injectors, for example, which use a mechanical force from a cam, such as the cam shaft, to actuate an injection valve. Engines using mechanical unit injectors typically include injector rocker arms to couple the cam to the mechanical unit injectors. The injector rocker arms pivot in response to rotation of the cam shaft, thereby to actuate the mechanical unit injector. In some of these systems, the injector rocker arm is configured to also engage the pin of the compression brake system. Accordingly, the same lobe of the cam shaft actuates both the mechanical unit injector and the compression brake system.
More recently, common rail systems have been used to inject fuel into the cylinders. The injector valves used in common rail systems are typically electronically actuated, and therefore do not require a mechanical source to actuate. Internal combustion engines having common rail systems, therefore, do not have injector rocker arms.